1. Field of the Invention
The present invention relates to the design and operation of a hot shelf tower dryer for a cotton gin. More specifically, the present invention concerns the placement of electrical heating elements at specific locations within a hot shelf dryer to augment the drying power of such a dryer.
2. Description of the Prior Art
Since it was invented by Eli Whitney more than a century ago, the cotton gin has remained the primary tool used to remove extraneous material, more commonly known as "trash," from newly-picked cotton. The "trash" removed typically includes seeds and other parts of the cotton plant that are collected together with the raw cotton when it is harvested. This "trash" must be separated from the cotton fibers before the fibers can be processed into thread and, ultimately, into fabric.
Cotton, however, is not ginned immediately after it is picked. Instead, among other pre-ginning processes, high moisture seed cotton is first partially dried in various types of apparatus known as a hot shelf tower dryer or a seed cotton dryer of some other type. The hot shelf tower dryer is a direct application of the knowledge that cotton is more easily ginned if a significant portion of the moisture contained in the cotton is first removed.
To dry cotton, the conventional hot shelf tower dryer includes a vertical tower casing, with substantially parallel shelf partitions. These shelf partitions alternately extend from one end wall of the tower casing to a location near the opposite end wall. So configured, the shelf partitions define a continuous zig-zag passage through the tower casing that guarantees a sufficient amount of drying by ensuring that the cotton remains in the dryer for a selected period of time at a desired temperature or range of temperatures.
In the conventional seed cotton dryer, cotton and heated air initially enter the hot shelf tower dryer through an inlet, located proximate to the top of the tower casing. The heated air carries the cotton through the convoluted path in the dryer to the outlet. As the cotton, which may have an initial moisture content of between about 15% to 20%, passes through the dryer, moisture is progressively driven from the cotton until the cotton exits the dryer with a moisture content of between about 11% to 16%. As many as three or four subsequent drying stages are needed to bring the cotton to a desired moisture content of between about 51/2% to 61/2%.
The heated air that carries the cotton through the dryer is inadequate, by itself, to dry the cotton sufficiently before it exits the dryer. This is because the initial exposure of wet cotton to the heated air results in a rapid evaporation of moisture from the seed cotton that robs the heated air of a significant portion of its thermal drying energy. As a result, the air becomes cooler. To compensate for the loss of drying energy associated with a reduced temperature, conventional hot shelf tower dryers include heated air ducts inside the shelves over which the seed cotton travels, as depicted in FIGS. 2 and 3. The heated air provided to these ducts or chambers supplies additional heat to the air in the tower casing to augment the drying process.
Both U.S. Pat. No. 4,031,593 and U.S. Pat. No. 5,233,764 describe hot shelf tower dryers with heated shelves that assist in drying seed cotton. As these disclosures provide, the shelves are heated by hot air circulated in the hollow interior chambers of the shelves. A push fan, which receives heated air from a remote heater, directs the heated air to and circulates this heated air within the shelf chambers.
In the conventional dryer design, because the heated air is generated remotely, there is a heat loss associated with the conveyance of the hot air to the shelf chambers. Depending upon the distance that the heated air must travel, this heat loss may be significant. The heater, as a result, must compensate for this temperature drop and, consequently, must increase the temperature of the heated air to a point higher than that required by the individual shelf chambers.
Typically, to attain a temperature of approximately 400.degree. F. in a chamber proximate to the inlet, a conventional heater, positioned beneath the outlet, may require an output temperature of approximately 900.degree. F. As expected, to attain such an increased level of heat requires the addition of a significant amount of energy to the heater.
Traditionally, natural gases or other fossil fuels have been used to heat the air for a seed cotton dryer. These natural resources, however, do not enjoy an unlimited surplus. As such, their consumption in providing the additional power to the heater involves both monetary as well as environmental waste.
In addition, these resources entail a fuel burning process that produces numerous pollutants in the form of gaseous emissions, such as nitrous oxide (NO.sub.x), the production of which has become increasingly restricted in an increasingly environmentally-conscious marketplace. The state of California is one such area where stringent regulations regarding fuel emissions have been implemented.
In this increasingly environmentally-conscious marketplace, the use of conventional burners to supply heat to the hot shelf tower dryer has become increasingly less desirable. The inability of the traditional hot shelf tower dryer and any other drying system to incorporate features that continue to provide the appropriate amount of cotton drying while reducing the amount of fuel consumed as well as the amount of fuel emissions produced has created a specific need for alternative techniques for mitigating temperature loss.
The present invention addresses these concerns by providing an apparatus that is practical and adaptable in both its design and application.